A colleague of mine who sees it below his dignity to ask question to his superior (helpful one) in his profession which he does not have know-how of, what would you call such a person ?
It encompasses "know-it-all" as in holier than thou,
"what-others-would-know-about-it" as in downplaying others and
"there-is-no-need-to-learn-these-things" as in sour grapes analogy.
"A colleague of mine is too imperious to ask questions of others that dare have more knowledge than him."
If you describe someone as imperious, you mean that they have a proud manner and expect to be obeyed; overbearing, arrogant, domineering, etc. Collins
I dont mean this in a bad way, but I really think you are confusing a bunch of things together. The four examples you gave all point towards different directions.
A "know-it-all", or a besserwisser as it's sometimes called (originally from German), is someone thinks s/he knows it all, and feels the need to show/share this knowledge with others by constantly correcting others or dropping tidbits at uncalled times.
Below his dignity to ask questions, would imply that the person can't be bothered to learn, that he cannot accept someone else is more knowledgeable.
Alternatively a person might be too shy to ask a question to a superior, not because of admitting their superiority but more for the fear of admitting to a lack of knowledge and possibly losing the other person's respect.
All in all, if the person in question has the attitude of "what could you possibly know more than me" towards a someone else I would probably start by calling that person arrogant and ignorant, as he would be ignoring and belittling others experience and knowledge.
If that person is additionally a superior (however you define that relationship) I would add the disrespectful and short-sighted, as well as expect him to be fired eventually if this all happens at a workplace :)
First to clear a few things up.
"know-it-all" /= holier than thou,
"what-others-would-know-about-it" /= downplaying others
I'm just going to drop the second half of those definitions rather than explain each of them ... I don't think they are what you're looking for, but they did help me guess what you are looking for.
I would rephrase your question
I am also going to side-step your title question as I'm not sure you really mean "below his dignity" To me that is more an emotional reaction like a senior developer assigned to program junior developers telephones, or considering working on the manual 'beneath him' - - If you want to point out his easy to hurt feelings .. perhaps that can be brought up separately from his failure to get the information he needs ?
A possible answer: close-minded
close-minded at freedictionary.com
Adj. 1. closed-minded - not ready to receive to new ideas
narrow-minded, narrow - lacking tolerance or flexibility or breadth of view; "a brilliant but narrow-minded judge"; "narrow opinions"
Is that perfect ? No ... but it is a bit less of a personal attack (less emphasis on ~social~ failure) while still pointing out work attitude that is counter-productive and perhaps dangerous.
You might combine it with another office euphemism if you wanted to dwell more on his personal reluctance to communicate
"close-minded and reluctant to seek input"
I would say that person is snobbish, or even condescending.
